LEDs offer benefits over incandescent and fluorescent lights as sources of illumination. Such benefits include high energy efficiency and longevity. To produce a given output of light, LEDs consume less energy than incandescent or fluorescent lights. Additionally, on average, LEDs last longer than incandescent or fluorescent lights before failing.
The level of light a typical LED outputs depends upon the amount of electrical current supplied to the LED and upon the operating temperature of the LED. That is, the intensity of light emitted by the LED changes according to electrical current and LED temperature. Operating temperature also impacts the usable lifetime of LEDs.
As a byproduct of converting electricity into light, LEDs generate heat and raise the operating temperature, resulting in efficiency degradation and premature failure. Typically, a heat management system, such as a heat sink, is used in conjunction with the LEDs to facilitate maintenance of proper LED operating temperatures. Conventional LED-based downlight luminaires include a housing, a heat sink, and one or more LEDs. The housing includes a cavity formed therein and an opening at one end. The housing is installed to or within a support structure, such as a ceiling, and oriented such that the opening faces a desired illumination area. The opening can be positioned in substantially the same plane as a surface of the support structure or alternatively in a different plane than the surface of the support structure. The heat sink for LED-based downlights is typically large to effectively remove heat away from the LEDs. The heat sink is installed and fitted within the cavity of the housing and substantially occupies the entirety of the available volume of the cavity to maximize its heat removal performance. Although heat sinks are constrained within the fixed volume of the housing when used in conjunction with an insulation contact (I.C.) rated housing, heat sinks can also be utilized within a non-fixed volume of the housing when used in conjunction with some types of non-insulation contact housings. The LEDs are typically coupled to a substrate, which is in thermal communication with the heat sink. The LEDs emit light and are oriented in a manner such that the light is directed to the desired illumination area through the opening. As a result of the heat sink occupying substantially all of the available volume of the cavity and the LEDs being thermally coupled to the heat sink, the LEDs are oriented in a fixed manner and are not directionally adjustable to provide flexibility in changing the desired illumination area.
According to one attempt that has been made to provide this flexibility, the heat sink has been made smaller to occupy less volume of the cavity, which thereby allows the heat sink and the LEDs coupled thereto to both translate in a particular direction. Since the heat sink is smaller, the performance of the smaller heat sink also is reduced. To accommodate for this reduced performance, fewer LEDs are coupled to the smaller heat sink and hence a lower light output is generated. Alternatively, the same number of LEDs are coupled to the smaller heat sink, but the performance and the longevity of the LEDs are adversely affected because the smaller heat sink is not large enough to effectively maintain the proper LED operating temperature. Additionally, the heat sink's range of movement is limited because although the heat sink has been made smaller, the heat sink is still relatively large and occupies a significant portion of the cavity's volume to remove the heat generated from the LEDs.